When calculating a discount rate if I have orginal contribution of $-1000$ a further contribution of $-819(-653$ when discount rate applied$)$ and $10$ distributions of $500$ each, then do I add sum of contributions $-1819$ to distributions $(500$x$10=5000)$ then divide by contibutions to give me the PME or is it $5000/1819$ or $5000/1653?$